1. Field of the Invention
The present invention relates to a steerable front wheel suspension for a vehicle and, more particularly, to a front wheel suspension for a vehicle which can increase a free layout degree with respect to a variation of a camber and caster, improve handling stability by providing a nominal kingpin and decreasing variation of a height of roll-center by means of a nominal link, and maximize the effective volume of an engine room by minimizing the space which the suspension system occupies.
2. Description of Related Art
In general, a suspension for a vehicle connects an axle shaft and a vehicle body to each other and controls a position of a wheel with respect to the vehicle body to obtain a better positioning in a vehicle operation. The axle shaft is thereby prevented from directly transmitting an impact or vibration from a road surface to the vehicle body, so that there can be obtained an optimal handling stability, a reduction in damage to baggage, and an improved ride comfort.
The suspension system is divided structurally into integral shaft suspension and independent suspension. The present invention relates to the independent suspension which can be divided into one of a McPherson strut type and a Wishbone type suspension system for a steering wheel.
Particularly, in a steerable front wheel suspension, the suspension should be designed to absorb vibration or impact from the road surface as well as obtain running stability by maintaining an optimal position of a vehicle's straight ahead position and handling stability of a vehicle's turning position.
The front wheel is mounted to change its direction from right to left or from left to right, while centering the kingpin, and is also mounted with a geometric angle so as to meet the requisite for the front suspension.
Mounting the front wheel with the geometric angle is called a front wheel alignment. The front wheel alignment is distinguished by several elements, but the optimal operation of the front wheel is, however, achieved by the supplemental operation of the elements with respect to each other. A kingpin inclination among the elements reduces a handling force of a steering wheel with a camber, absorbs an impact generated when the vehicle is running and being braked, and then increases restitution force of a steering wheel, thereby obtaining running stability in the vehicle's straight ahead position and handling stability in the vehicle's turning position.
The kingpin is mounted at an inclination such that its central line lies at a predetermined angle with respect to the vertical line when the vehicle is viewed from the front. An interval between the center line of the kingpin and a center line of the wheel is called offset. The offset is generally characterized as an offset at the wheel center and an offset at the ground. The offset at the wheel center has an effect on the vehicle's straight ahead running characteristics when either the driving force or the engine brake is applied to the wheels. The offset at the ground has an effect on the handling stability when the vehicle is braking and turning. If the offset at the ground is decreased, sensitivity with respect to the steering is decreased, such that the handling stability is increased when the vehicle is cornering and being braked.
Further, stability of the vehicle is closely related to the vibration of the car body. During the vehicle's running, rolling, pitching, and yawing occurs in addition to bounce. These vibrations should be absorbed to increase the stability and ride comfort of the vehicle.
In such vibrations, the rolling occurs at a predetermined point when the vehicle is in a turning situation, and this point is called a roll center. The variation rate of the roll center's height has an effect on the running stability and handling stability of the vehicle. Accordingly, to achieve running stability, it is more desirable to decrease the variation rate of the roll center's height.
FIG. 6A is a schematic diagram of a conventional McPherson type strut, wherein the suspension includes a strut assembly 73 having a shock absorber 72 and a spring 74 and being integrally formed with a knuckle 71, a lower arm 75, and a ball joint 76.
This suspension has an advantage in its simple structure and weight. To reduce the kingpin offset A or attain a negative (-) state, an upper supporting point of the strut assembly 73 must be moved to the engine room, or the ball joint portion 76 must be moved to an outside of the engine room. However, in the case where the upper supporting point is moved to the engine room, the available volume of the engine room is to be reduced simultaneously with increasing a kingpin angle .alpha. thereby having a bad effect on the cornering performance of the vehicle. Also, it is impossible to move the ball joint portion 76 outside of the engine room because of being interfered with by a disk brake. Therefore, this suspension has a problem in reducing the kingpin offset.
FIG. 6B is a schematic diagram of a conventional Wishbone type suspension system, wherein the suspension includes upper and lower control arms 81 and 82; a steering knuckle 83; a spring assembly 85 having a shock absorber 84; and ball joints 86 and 87 of the upper and lower control arms 81, 82.
Like the McPherson type described above, when connecting point 88 of the upper control arm 81 is moved to the engine room, the available volume of the engine room is reduced when increasing the kingpin offset .alpha.. The cornering performance of the vehicle may be adversely affected thereby. And also, it is next to impossible to move the ball joint 87 of the lower control arm 82 outside of the engine room because of being interfered with by a disk brake. Therefore, this suspension system also has a problem in reducing the kingpin. Conventional McPherson type and Wishbone type suspension systems have such a small range for the free layout degree of kingpin, that it is impossible to reduce the kingpin offset and there is a limit to improving the function of the suspension system.
Because the up-down movement of a wheel relies on a small arm and the variation rate of the roll center's height is high, the running stability is not good.